Robot fingers integrated with force sensors can perform complex grasping tasks [2]. A surgical cutting tool has been connected to a three-axes force sensor for accurate force sensing in fetal surgery [3].There are several approaches to the design and fabrication of force sensors. Two and three dimensional cantilever and capacitive [4] force sensors have been studied in detail in the past. Cantilevers can measure only in 2 D, whereas capacitive force sensors are very complex due to the compulsory electronic circuits for capacitance detection. There are other optical- and laser-based measurements on multi-sensor systems which provide highly accurate measurement on visible surfaces, but it is difficult to use these systems for 3D measurements.

This is an important reason why many groups are working on developing a tactile sensor using a four arm structure [5-8] for contact probing.As far as the state of the art of 3D silicon-based force sensors is concerned, they have been developed mainly using the piezoresistive and capacitive sensing principles. Chu et al. [9] reported on a 3D tactile sensor based on the differential capacitive principle, where the measuring range and the sensitivity could be adjusted by changing the membrane’s thickness. Fabrication is quite complicated due to combination of elastomer, silicon, glass and polymer, which is simplified in this work by only using silicon. There is offset in output signal due to anodic bonding used in the fabrication, also the cross talk cannot be neglected, because four electrodes are used.

Recently, a 3D force sensor has been fabricated using a titanium foil, where a stylus is attached to the centre of the symmetrical four-arm titanium foil structure [5]. The Dacomitinib drawback is that the strain gauges are individually glued onto the titanium foil which leads to variations in the position of the strain gauges on the foil. Strain gauge position variations lead to sensitivity variation from sensor to senor. Here, the strain gauges are diffused in the membrane thus positioning uncertainty is almost negligible.In this work, we have simulated, fabricated and characterized miniaturized three-axes piezoresistive force sensors with 16 p-type piezoresistors on the boss membrane structure, which are connected in a Wheatstone bridge form. The sensitivity of the sensors can be enhanced by optimally designing the membrane structure. We have fabricated and characterized five different membrane designs.Here, various results for e.g. sensitivity in x, y and z direction, maximum and minimum deflections and resonance frequency of each designs are measured and summarized. Simulations were performed by varying the length of the stylus to study its impact on H:V stiffness ratio and deflection in the membrane.